The present invention relates generally to dampers, and more particularly, to a thermal operator for use with such dampers.
A problem commonly encountered in the use of many heating systems such as oil and gas fired home and hot water heaters, as well as with wood and coal burning stoves and fireplaces, is that smoke and gas fumes are produced. These smoke and gas fumes must therefore be vented to the outside through a chimney or flue. This venting is done both to create the proper draft conditions for combustion and to avoid creating conditions hazardous to the inhabitants of the building where the the heating systems are used. However, such venting creates a permanent opening which, when the heating system is not in use, allows heat to escape from the structure being heated. This creates the potential for considerable energy losses and considerable unnecessary operating expenses.
To solve these problems, a variety of dampers have been developed which can be fitted into the vent chimney of heating systems to block the vent opening in a manner which conserves residual heat contained within the building, thus reducing the rate of fuel consumption. Essentially, such dampers generally used an external sensor to activate the damper operator and thereby open or close the damper to vent fumes a needed and conserve heat the rest of the time. For example, U.S. Pat. No. 4,123,001 issued to Kolt, and U.S. Pat. No. 3,921,900 issued to Cole, both show bellows activated systems for use with such dampers. U.S. Pat. No. 4,205,783 issued to Dietsch, discloses spring biasing means for use with a motor operated damper.
However, the problems and expenses encountered in adapting such activator systems to a particular damper and its associated chimney structure, as well as the cost of the power frequently required to operate such activator systems, can be sufficient to make the systems uneconomical. These costs may even be higher than the savings afforded by the reduction in losses which is provided by the damper.
It is therefore preferable that the damper be self-activating, so that when it is placed into a vent or flue, the damper can respond directly and automatically to the presence or absence of heat or pressure to open or close by itself. Using such a system no external source of power is required, providing substantial savings in costs. Moreover, this permits such a damper to be located in places where excessive heat loads exist. These heat loads can quickly degrade the electrical sensor wiring, of remotely controlled units. Additionally, automatic units can be used where external power lines are difficult or expensive to install. Further, such dampers were easier to adapt to a wide variety of operating conditions with a minimum of alteration or modifications. Such capabilities provided sufficient savings to make them economical, both in the initial fabrication of the damper, as well as in the field installation and ultimate use of the damper.
One approach which has been used in a effort to meet this need for a self-activating damper involves the use of a large, slotted flap or a plurality of interleaved bimetallic flaps, usually four, which are reciprocally positioned to be opened or closed according to the ambient temperature within the flue. However, such a self-activating device tends to suffer from a number of disadvantages. For example, each flap of the device must be self-activating, and therefore must be fabricated from relatively expensive bimetallic materials. Moreover, such materials, while flexible to some degree, are generally unable to completely fold out of the path of exiting smoke or gas fumes. Thus the flaps create a chimney restriction when the damper is opened. This restriction, at best, reduces surface efficiency by reducing chimney draft. At times this type of restriction can even cause smoke and gaseous combustion products to back up within the system and escape into the building thereby endangering inhabitants of the building.
Another disadvantage of such a damper is that the flaps must be specifically sized in order for the damper to be useful in a variety of applications. This adds to the normal scrap losses encountered in producing such a damper and adds significantly to its cost of production.
Lastly, bimetallic material is relatively stiff. As a result, flaps manufactured using such materials do not respond quickly. Because of this, in furnaces in which an increase of pressure can occur before an increase of temperature, for example, oil fire furnaces, such flaps are unable to open quickly enough to relieve the pressure produced. It is for this reason that such damper systems are not recommended for use with oil fire furnaces.
It is therefore desirable to provide a damper having a self-actuating damper operator which can be constructed of low cost, general purpose components, yet which is readily adaptable to a wide variety of installation situations and operational conditions. Such a system would significantly reduce, the foregoing problems. A solution to this problem is suggested in U.S. Pat. No. 4,372,485 issued to McCabe on Feb. 8, 1983 and titled "Thermally Activated, Automatic Damper and Damper Operator". The damper operator of McCabe is a butterfly type damper, constructed primarily to perform as an air, smoke and fire damper as described in U.S. Pat. No. 4,146,048 issued Mar. 27, 1979 and entitled "Fire Damper and Method of Construction" and U.S. Pat. No. 3,889,314 issued June 17, 1975 and entitled "Heat Actuated Link". All three of these patents, U.S. Pat. Nos. 4,372,485, 4,146,048, and 3,889,314 are incorporated by reference as if fully set forth herein.
In the thermally activated automatic damper of U.S. Pat. No. 4,372,485, the butterfly damper includes a pair of complementary damper blades which are engaged by hinge elements on a cross bar extending across the length of the damper frame to bridge the duct in which the damper is installed. If preferred, the cross bar may also be directly attached to the opposing side walls of the duct. In the fully opened position, the damper blades are caused to assume a position in which they are substantially parallel to one another, and to the air flow through the duct. This minimizes resistance to the air flow through the duct In the fully closed position, the damper blades and the cross bar combine to substantially seal the duct. The frame, blade and cross bar components are readily adaptable for use in varied applications.
The damper is provided with a self-actuating damper operator mechanism which generally comprises a bimetallic, serpentine thermal spring element. One end of the bimetallic element is attached to the cross bar and the other end is pivotally connected to the blades of the damper by a pair of linkages. The operation of the damper occurs when the ambient temperature surrounding the thermal spring element changes.
For example, the damper and damper operator of the thermally activated system can be used in a flue damper. In such a case, when the thermal spring element is cooled, the damper operator is set to assume its closed position. As the element is heated its bimetallic structure causes it to flex. This flexing causes the attached linkages to rotate the damper blades to their open positions. When the thermal spring element is cooled, the reverse effect occurs and the blades are again closed. This operation is continuous and passive, since no external sensors or power source are needed to obtain these results except the heat rise.
The thermally activated automatic damper could also be used with other types of dampers, for example, ceiling mounted smoke/fire dampers. In such an application, the damper is generally provided to complement a fire rated secondary ceiling to prevent heat damage to the primary ceiling and its structural support for a rated time period. For smoke vent dampers, the thermal spring element is caused to operate as described above, causing the blades to open when heated, to permit smoke to escape from the room, and to close when cooled. For fire dampers, operation of the thermal spring element is reversed, so that the blades close when heated and open when cooled.
Dampers of this type can also be used to provide damper control for use in air conditioning systems. In air conditioning applications the dampers respond to changes in room temperature in such a way that the conditioned air admitted to a selected area can be regulated to maintain a uniform temperature therein. However, in such an application it is generally necessary to avoid systems imbalances by assuring that there is always some minimum amount of air being admitted to an area. This is accomplished by providing a thermal spring element with means for volume adjustment. The volume adjustment assures that the blades of the damper remain open a sufficient amount of time to maintain a proper flow through the air duct within which the damper is placed.
Additionally, in pilot operated systems for remotely controlled systems, a further remote operator can be provided for use with the thermally activated automatic damper to further control the opening and closing of the damper in order to remotely maintain stable operating conditions within the systems.
However, in systems using the thermally activated automatic dampers it is difficult to control the fully closed position. This is important where economic considerations require a damper design which can be used in a number of different applications which require differing amounts distance between the "fully closed" positions of the blades and the actual sealing position of the damper to provide differing air flow conditions.
Additionally, the response time and the speed of the opening and closing of the damper blades in the prior art automatic thermally activated dampers, as well as the temperature at which the dampers actuated could not be conveniently controlled and modification of the response time and the speed of opening and closing of the blades and the actuated temperature are important in designing dampers.
Thus it is an object of the present invention to provide a thermally activated automatic damper wherein the fully closed position of the damper can be conveniently and reliably controlled.
It is a further object of the present invention to provide a thermally activated automatic damper wherein the response time and the speed and temperature of opening and closing operation of the damper can be controlled.